Production of hydrocarbons from reservoirs is usually done through a well drilled from surface to the reservoir. Such a well is cased to prevent collapse of its wall. To facilitate fluids flowing into the well, the part of the well extending into or through the reservoir is either not cased or, when cased, the casing is perforated locally. If the underground formation includes sandstone, production of hydrocarbons may cause formation minerals such as sand to be loosened and to be entrained by the fluids flowing into the well, particularly after water break through. The entrained materials cause wear of production equipment through which the fluid passes, and it is expensive to separate and to dispose the material. To reduce the amount of entrained materials, the formation is strengthened using an epoxy resin system.
A problem is encountered when the underground formation includes "dirty" sand. Dirty sand is sand which is covered with contaminants such as hydrocarbon oil and water. The presence of these contaminants will adversely affect the bond between the sand particles and the epoxy resin and consequently the strength of the treated formation.
U.S. Pat. No. 3,481,403 suggests a method of treating an underground formation which includes the steps of contacting the underground formation with a solvent in the form of an alkyl ether of a C.sub.2 to C.sub.6 glycol containing at least one C.sub.1 to C.sub.6 alkyl group, and thereafter contacting the formation with a consolidation solution of an epoxy resin and a curing agent in a solvent of alcohol-kerosene. The solvent may be preceded by an oil preflush to remove water blocks. Moreover, if the formation has already produced large volumes of sand, a suspension of sand in water or oil can be injected before the treating starts to complement the lost sand.
U.S. Pat. No. 3,915,232 discloses a method of treating an underground formation comprising the sequential steps of:
(a) contacting the formation with an aqueous medium; PA1 (b) contacting the formation with a hydrocarbon fluid in order to displace water; and PA1 (c) contacting the formation with a solvent in the form of a glycol ether in order to displace the residual hydrocarbon and water. PA1 (a) contacting the formation with an aqueous medium; PA1 (b) contacting the formation with a hydrocarbon fluid; PA1 (c) contacting the formation with a solvent in the form of a mixture of glycol ethers; PA1 (d) contacting the formation with a consolidation solution of between 30 and 60% m (per cent by mass) of monomeric and/or polymeric organic polyepoxides having more than one epoxy group per molecule and between 5 and 20% m of a curing agent in the solvent; and PA1 (e) contacting the formation with a viscosified fluid containing aliphatic hydrocarbons.
In this known method a sand screen of bonded sand grains is to be placed in a well in the annulus between the casing and the formation. Therefore, in step (a) of the known method a slurry of sand in brine is injected through perforations in the casing into the well in order to place the sand behind the casing in the annulus. In order to bond the sand grains to form a screen, a consolidation solution containing an epoxy resin and a catalyst is injected through the perforations in the casing. The solvent used in the consolidation solution is a different solvent than the glycol ether used to displace the residual hydrocarbon and water.
European patent application publication No. 463 664 discloses a method of treating an underground formation, wherein the consolidation solution comprises polyepoxides, a curing agent, a glycol ether and a polyalkylene glycol. The treatment can be followed by an over-flush of a hydrocarbon solvent mixture to remove excess resin. It would be desirable to increase the epoxide-content of the consolidation solution without affecting the viscosity.
It is an object of the present invention to improve the above described method. It is a further object to provide a method for treating an underground formation a consolidation solution with a large concentration of epoxy resin can be used.